Reducing internal node loading in combination circuits

ABSTRACT

Circuit devices, such as integrated circuit devices, are constructed with combination circuits that include two or more cascading transistors, and one or more metal layers disposed over the cascading transistors. The cascading transistors include multiple internal nodes (e.g., common source/drain regions). The multiple internal nodes are not connected to a common metal stripe (the same metal stripe) in the one or more metal layers. The absence of the connections between the internal nodes and a common metal stripe reduce or eliminate the load on the internal nodes. The transistors in the cascading transistors are independent of each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/173,750,filed Feb. 11, 2021, the entire content of which isincorporated herein by reference.

BACKGROUND

Over the last several decades the semiconductor fabrication industry hasbeen driven by a continual demand for greater performance (e.g.,increased processing speed, memory capacity, etc.), a shrinking formfactor, extended battery life, and lower cost. In response to thisdemand, the industry has continually reduced a size of semiconductordevice components, such that modern day integrated circuit (IC) devicesmay comprise millions or billions of semiconductor devices arranged on asingle semiconductor die.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood by the followingdetailed description in conjunction with the accompanying drawings,where like reference numerals designate like structural elements. It isnoted that various features in the drawings are not drawn to scale. Infact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 depicts a block diagram of an example integrated circuit devicein which aspects of the disclosure may be practiced in accordance withsome embodiments;

FIG. 2 illustrates a layout of a portion of an integrated circuit inaccordance with some embodiments;

FIG. 3 depicts a cross-sectional view taken along line A-A of theportion of the integrated circuit shown in FIG. 2 in accordance withsome embodiments;

FIG. 4 illustrates a schematic diagram of a NAND circuit in accordancewith some embodiments;

FIG. 5 depicts an example layout of the NAND circuit shown in FIG. 4 inaccordance with some embodiments;

FIG. 6 illustrates a schematic diagram of a NOR circuit in accordancewith some embodiments in accordance with some embodiments;

FIG. 7 depicts an example layout of the NOR circuit shown in FIG. 6 inaccordance with some embodiments;

FIG. 8 illustrates an example third combination circuit that includescascading n-type transistors in accordance with some embodiments;

FIG. 9 depicts an example fourth combination circuit that includescascading p-type transistors in accordance with some embodiments;

FIG. 10 illustrates a flowchart of an example method of designing anintegrated circuit in accordance with some embodiments;

FIG. 11 depicts a set of bus naming rules for a three-input NAND circuitin accordance with some embodiments;

FIG. 12 illustrates a set of cascading transistors that is defined bythe set of bus naming rules shown in FIG. 11 in accordance with someembodiments;

FIG. 13 depicts an example system that is suitable for designing anintegrated circuit in accordance with some embodiments;

FIG. 14 illustrates a flowchart of an example method of fabricating aset of cascading transistors in accordance with some embodiments;

FIG. 15 depicts the set of cascading transistors shown in FIG. 4 afterthe method of FIG. 14 is performed in accordance with some embodiments;

FIG. 16 illustrates the set of cascading transistors shown in FIG. 6after the method of FIG. 14 is performed in accordance with someembodiments; and

FIG. 17 depicts a block diagram of an example integrated circuitmanufacturing system and manufacturing flow in accordance with someembodiments,

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “over,” “under”, “upper,” “top,” “bottom,” “front,” “back,” andthe like, may be used herein for ease of description to describe oneelement or feature's relationship to another element(s) or feature(s) asillustrated in the Figure(s). The spatially relative terms are intendedto encompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. Because componentsin various embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration only and is in no way limiting. When used in conjunctionwith layers of an integrated circuit, semiconductor device, orelectronic device, the directional terminology is intended to beconstrued broadly, and therefore should not be interpreted to precludethe presence of one or more intervening layers or other interveningfeatures or elements. Thus, a given layer that is described herein asbeing formed on, over, or under, or disposed on, over, or under anotherlayer may be separated from the latter layer by one or more additionallayers.

Integrated circuits are commonly used in various electronic devices.Integrated circuits typically include combination circuits that provideor contribute to the functionality or functionalities of the integratedcircuit. A combination circuit is a circuit that includes one or moreset of cascading transistors, where the number of transistors in eachset of cascading transistors is greater than one. Example combinationcircuits include, but are not limited to, logic components such as aflip flop, latch, NAND, OR, AND, and NOR circuits. Many of thecombination circuits include two or more cascading transistors, such as,for example, cascading metal-oxide semiconductor (MOS) transistors.

In some integrated circuits, all of the cascading transistors in acombination circuit are connected to the same metal stripe in a metallayer, such as a metal stripe in an M0layer. Since the cascadingtransistors are formed in the same active diffusion region (e.g., an ODregion), have the same gates, and are connected to the same metalstripe, the cascading transistors are identical to each other but arenot independent of each other. Additionally, the connections to the samemetal stripe in the metal layer increase the load on each internal nodein the cascading transistors. For example, two cascading transistors areformed when the transistors are connected in series. The internal nodeis the connection between a terminal (e.g., S/D region) of the firsttransistor and a terminal (e.g., S/D region) of the second transistor,which is the connection at the common source/drain region. When thecascading transistors are connected to the same metal stripe (e.g.,using a via-to-diffusion (VD) connection), the load on the internal nodeis increased, which in turn can adversely impact the performance of thecombination circuit. For example, the power consumption and/or the delaytiming of the combination circuit can increase.

Embodiments disclosed herein provide layouts for combination circuitsthat reduce or eliminate the load on each internal node in a set ofcascading transistors. As described herein, the load on each internalnode can be reduced or eliminated by constructing the cascadingtransistors in an active diffusion region without connecting theinternal nodes to the same metal stripe in the same metal layer (e.g.,the M0layer). In such a construction, the cascading transistors are bothidentical and independent of each other.

The embodiments described herein are described with respect to metallayers, metal stripes, poly layers, and poly lines. However, otherembodiments are not limited to metal layers, metal stripes, poly layers,and poly lines. Any suitable conductor that is made of one or moreconductive materials can be used. Additionally, the conductors can beformed in one or more conductor layers.

These and other embodiments are discussed below with reference to FIGS.1-10. However, those skilled in the art will readily appreciate that thedetailed description given herein with respect to these Figures is forexplanatory purposes only and should not be construed as limiting.

FIG. 1 depicts a block diagram of an example integrated circuit in whichaspects of the disclosure may be practiced in accordance with someembodiments. The illustrated integrated circuit is a memory device 100,although other embodiments are not limited to this type of an integratedcircuit. Any integrated circuit or combination circuit that includescascading transistors can employ the invention.

The memory device 100 includes memory cells 102 that are arranged inrows and columns to form a memory array 104. The memory device 100 caninclude any suitable number of rows and columns. For example, a memorydevice includes R number of rows and C number of columns, where R is aninteger greater than or equal or one and C is a number greater than orequal to one. Other embodiments are not limited to rows and columns ofmemory cells 102. The memory cells 102 in a memory array 104 can beorganized in any suitable arrangement.

Each row of memory cells 102 is operably connected to one or more wordlines (collectively word line 106). The word lines 106 are operablyconnected to one or more row select circuits (collectively referred toas row select circuit 108). The row select circuit 108 selects aparticular word line 106 based on an address signal that is received onsignal line 110.

Each column of memory cells 102 is operably connected to one or more bitlines (collectively bit line 112). The bit lines 112 are operablyconnected to one or more column select circuits (collectively referredto as column select circuit 114). The column select circuit 114 selectsa particular bit line 112 based on a select signal that is received onsignal line 116.

A processing device 118 is operably connected to the memory array 104,the row select circuit 108, and the column select circuit 114. Theprocessing device 118 is operable to control one or more operations ofthe memory array 104, the row select circuit 108, and the column selectcircuit 114. Any suitable processing device can be used. Exampleprocessing devices include, but are not limited to, a central processingunit, a microprocessor, an application specific integrated circuit, agraphics processing unit, a field programmable gate array, orcombinations thereof.

A power supply 120 is operably connected to the memory array 104 and theprocessing device 118. In some embodiments, the power supply 120 is alsooperably connected to the row select circuit 108 and the column selectcircuit 114. The processing device 118 and/or the power supply 120 canbe disposed in the same circuitry (e.g., macro) as the memory array. Inan example embodiment, the macro refers to a memory unit that includesthe memory array and peripherals such as the control block, input/outputblock, row decoder circuitry, column decoder circuitry, etc. In otherembodiments, the processing device 118 and/or the power supply 120 maybe disposed in separate circuitry and operably connected to the macro(e.g., the memory array).

When data is to be written to a memory cell 102 (e.g., the memory cell102 is programmed), or is to be read from a memory cell 102, an addressfor the memory cell is received on signal line 110. The row selectcircuit 108 activates or asserts the word line 106 associated with theaddress. A select signal is received on the signal line 116 and the bitline 112 associated with the select signal is asserted or activated. Thedata is then written to, or read from, the memory cell 102.

The memory device 100, the row select circuit 108, the column selectcircuit 114, the processing device 118, and the power supply 120 areincluded in an electronic device 122. The electronic device 122 can beany suitable electronic device. Example electronic devices include, butare not limited to, a computing device such as a laptop computer and atablet, a cellular telephone, a television, an automobile, a stereosystem, and a camera.

The memory device 100 typically includes one or more combinationcircuits that are constructed with one or more sets of cascadingtransistors. For example, one or more of the memory array 104, the rowselect circuit 108, the column select circuit 114, the processing device118, and/or the power supply 120 includes at least one or more sets ofcascading transistors. Each set of cascading transistors can include twoor more transistors. In some embodiments, the transistors in a set ofcascading transistors has a size defined by (2fin×m), where m is thenumber of the cascading transistors in the set, m is greater than one,and the number of internal nodes is greater than one. Some or all of thecombination circuits may employ the present invention.

FIG. 2 illustrates a layout of a portion of an integrated circuit inaccordance with some embodiments. The layout 200 includes a first activediffusion region 202 and a second active diffusion region 204 that aredisposed in the y direction. Polysilicon (“poly”) lines 206 a, 206 b,206 c, 206 d are disposed in the x direction over the first and thesecond active diffusion regions 202, 204. The first and the secondactive diffusion regions 202, 204 can include fin structures that aredisposed on a substrate (not shown) and serve as active regions of thetransistors (e.g., source/drain regions). The poly lines 206 a, 206 b,206 c, 206 d act as gates for the transistors.

A first metal layer 208 (e.g., the M0 layer) is disposed over the firstactive diffusion region 202, the second active diffusion region 204, andthe poly lines 206 a, 206 b, 206 c, 206 d. In the illustratedembodiment, the first metal layer 208 includes metal stripes 208 a, 208b, 208 c, 208 d, 208 e, 208 f, 208 g. In a non-limiting example, themetal stripes 208 a, 208 g provide one or more voltage sources (e.g.,VDD and VSS) and the metal stripes 208 b, 208 c, 208 d, 208 e, 208 f areused for various signals.

The first metal layer 208 is a metal layer at the bottom of a pluralityof metal layers (e.g., an M0 layer). In the illustrated embodiment, thefirst metal layer 208 is positioned below a second metal layer 210(e.g., an M1 layer), and the second metal layer 210 is disposed below athird metal layer 212 (e.g., an M2 layer). The first metal layer 208,the second metal layer 210, and the third metal layer 212 form a stackof metal layers. Other embodiments are not limited to three metal layersin the stack of metal layers. Any number of metal layers can be includedin a stack of metal layers.

As shown in FIG. 2, the first metal layer 208 is positioned between anoverlying second metal layer 210 and the underlying first activediffusion region 202, the second active diffusion region 204, and thepoly lines 206 a, 206 b, 206 c, 206 d. The second metal layer 210includes example metal stripes 210 a, 210 b, 210 c. The second metallayer 210 is disposed between an overlying third metal layer 212 and theunderlying second metal layer 210. The third metal layer 212 includesexample metal stripes 212 a, 212 b, 212 c. Other embodiments can includeany number of metal stripes in the first metal layer 208, the secondmetal layer 210, and the third metal layer 212.

The first and the second active diffusion regions 202, 204 (e.g., oxidediffusion (OD) regions) include fin structures that are disposed on asubstrate (not shown) and serve as active regions of the transistors inthe integrated circuit. Specifically, the fin structures serve aschannel regions of the transistors when positioned below the polysilicon(“poly”) lines 206 a, 206 b, 206 c, 206 d and/or serve as source/drain(S/D) regions when positioned below the metal stripes. In a non-limitingexample, the first active diffusion region 202 is an S/D region forp-type transistors and the second active diffusion region 204 is an S/Dregion for n-type transistors. In the illustrated embodiment, one ormore of the nodes represent an internal node 214, 216, 218 in a set ofcascading transistors, where the set of cascading transistors includestwo or more cascading transistors. As is described in more detail later,the load on the internal nodes 214, 216, 218 is reduced or eliminatedbecause the internal nodes 214, 216, 218 are not connected to the samemetal stripe (a “common metal stripe”) in any of the first, the second,or the third metal layers 208, 210, 212 in the metal stack.

FIG. 3 depicts a cross-sectional view of a portion of the integratedcircuit shown in FIG. 2 in accordance with some embodiments. The polylines 206 a, 206 b, 206 c, 206 d are disposed over the first activediffusion region 202. The metal stripe 208 c in the first metal layer ispositioned over the poly lines 206 a, 206 b, 206 c, 206 d and the firstactive diffusion region 202. In the illustrated embodiment, transistors300, 302, 304, 306 form a set 307 of cascading transistors that includethe internal nodes 214, 216, 218. A terminal (e.g., S/D region) of thetransistor 300 is connected to a terminal (e.g., S/D region) of thetransistor 302 at the internal node 214 (e.g., the common S/D region308). A terminal (e.g., S/D region) of the transistor 302 is connectedto a terminal (e.g., S/D region) of the transistor 304 at the internalnode 216 (the common S/D region 310). A terminal (e.g., S/D region) ofthe transistor 304 is connected to a terminal (e.g., S/D region) of thetransistor 306 at the internal node 218 (the common S/D region 312).Transistors 300, 302, 304, 306 are identical in that the transistors300, 302, 304, 306 are formed in the same active diffusion region (e.g.,same S/D regions) and have the same gates.

As shown in FIG. 3, a connection between the metal stripe 208 c and theinternal node 214 is absent (see highlighted area 314), a connectionbetween the metal stripe 208 c and the internal node 216 is absent (seehighlighted area 316), and a connection between the metal stripe 208 cand the internal node 218 is absent (see highlighted area 318). The loadon the internal nodes 214, 216, 218 is reduced or eliminated due to thelack of connections to a common metal stripe (e.g., metal stripe 208 cin the first metal layer). Additionally, the transistors 300, 302, 304,306 are independent of each other since the internal nodes 214, 216, 218are not connected to the same metal stripe (the connections between themetal stripe 208 c and the internal nodes 214, 216, 218 do not exist).Further, the internal nodes 214, 216, 218 are not connected to a commonmetal stripe in any of the metal layers overlying the first metal layer(e.g., metal layers 210, 212 in FIG. 2).

As noted earlier, an integrated circuit typically includes a variety ofcombination circuits that include cascading transistors. FIG. 4illustrates an example first combination circuit in accordance with someembodiments. The example first combination circuit 400 is a NANDcircuit. The first combination circuit 400 includes a transistor 402connected in series with a transistor 404. In the illustratedembodiment, the transistors 402, 404 are n-type transistors, and oneexample of an n-type transistor is an NMOS transistor. A terminal (e.g.,S/D region) 406 of the transistor 404 is connected to a voltage source408 (e.g., VSS or ground). A terminal (e.g., S/D region) 410 of thetransistor 404 is connected to a terminal (e.g., S/D region) 412 of thetransistor 402 at an internal node 414. The first and the secondtransistors 402, 404 are cascading transistors and form a set 415 ofcascading transistors.

A transistor 416 is connected in parallel with a transistor 418. In theillustrated embodiment, the transistors 416, 418 are p-type transistors,and one example of a p-type transistor is a PMOS transistor. Thetransistor 416 is also connected in series with the transistor 402. Aterminal (e.g., S/D region) 420 of the transistor 416 and a terminal(e.g., S/D region) 422 of the transistor 418 are connected to a voltagesource 424 (e.g., VSS or ground). A terminal (e.g., S/D region) 426 ofthe transistor 416, a terminal (e.g., S/D region) 428 of the transistor418, and a terminal (e.g., S/D region) 430 of the transistor 402 areconnected together at node 432. An output signal line 434 is connectedto node 432.

The transistors 402, 404, 416, 418 can be constructed with any suitablenumber of fins. Some or all of the transistors 402, 404, 416, 418 aren×m transistors, where the variable n represents the number of fins andthe variable m represents the number of transistors. For example, in oneembodiment, the transistors 402, 404 are implemented as 2×2 transistors(2 fins, two transistors). Thus, each transistor 402, 404 in FIG. 4represents two transistors (for a total of four transistors). In anotherembodiment, the transistors 402, 404 are implemented as 2×4 transistors(2 fins, four transistors), and each transistor 402, 404 is fourtransistors (for a total of eight transistors).

FIG. 5 depicts an example layout of the first combination circuit shownin FIG. 4 in accordance with some embodiments. The example layout 500represents an embodiment where the transistors 402, 404 are implementedas 2×4 transistors (2 fins, four transistors). The layout 500 includesan active diffusion region 502 (e.g., active diffusion region 202 inFIG. 2) disposed in the y direction. As described earlier, the activediffusion region 502 includes one or more fin structures that aredisposed on a substrate (not shown) and serve as the active regions ofthe transistors 402, 404(FIG. 4). The illustrated active diffusionregion 502 includes the n-type well region and the fins for the n-typetransistors 402, 404.

Poly lines 504, 506, 508, 510, 512, 514, 516, 518 are disposed over theactive diffusion region 502 in the x direction. Poly lines 504, 510,512, 518 function as the gate B for the four transistors 404 a, 404 b,404 c, 404 d, respectively, (see FIG. 4) in the set 415. The S/D region406 is represented above the poly line 504, below the poly line 518, andbetween the poly lines 510, 512.

The common S/D region 410, 412 is positioned below the poly line 504 andabove the poly line 506, below the poly line 508 and above the poly line510, below the poly line 512 and above the poly line 514, and below thepoly line 516 and above the poly line 518. The common S/D regions 410,412 are the internal nodes 414 a, 414 b, 414 c, 414 d.

The poly lines 506, 508, 514, 516 act as the gate A for the fourtransistors 402 a, 402 b, 402 c, 402 d in the set 415. S/D region(“OUT”) 430 of the four transistors 402 a, 402 b, 402 c, 402 d is shownbelow the poly line 506 and above the poly line 508 and below the polyline 514 and above the poly line 516.

Although not shown in FIG. 5, a stack of metal layers (e.g., first metallayer 208, second metal layer 210, and third metal layer 212 shown inFIG. 2) is disposed over the active region 502 and the poly lines 504,506, 508, 510, 512, 514, 516. The layout 500 does not include aconnection between the internal nodes 414 a, 414 b, 414 c, 414 d and acommon (e.g., the same) metal stripe in any of the metal layers in thestack of metal layers. For example, there are no connections between theinternal nodes 414 a, 414 b, 414 c, 414 d and a common metal stripe inthe first metal layer. The functions of the transistors 402 a, 402 b,402 c, 402 d, 404 a, 404 b, 404 c, 404 d are the same as conventionaltransistors, but the connections between the internal nodes 414 a, 414b, 414 c, 414 d and a common metal stripe in a metal layer (e.g., M0layer) in the stack of metal layers is absent. Each internal node 414 a,414 b, 414 c, 414 d is independent of the other internal nodes 414 a,414 b, 414 c, 414 d, and the loading on the internal nodes 414 a, 414 b,414 c, 414 d is reduced or eliminated due to the nonexistent connectionbetween a common metal stripe and the internal node 414. Additionally,the transistors 402 a, 402 b, 402 c, 402 d 404 a, 404 b, 404 c, 404 dare both identical and independent of each other.

FIG. 6 illustrates an example second combination circuit in accordancewith some embodiments. The example second combination circuit 600 is aNOR circuit. The second combination circuit 600 includes a transistor602 connected in series with a transistor 604. In the illustratedembodiment, the transistors 602, 604 are p-type transistors, and oneexample of a p-type transistor is a PMOS transistor. A terminal (e.g.,S/D region) 606 of the transistor 602 is connected to a voltage source608 (e.g., VSS). A terminal (e.g., S/D region) 610 of the transistor 602is connected to a terminal (e.g., S/D region) 612 of the transistor 604at an internal node 614. The first and the second transistors 602, 604are cascading transistors and form a set 615 of cascading transistors.

A transistor 616 is connected in parallel with a transistor 618. Thedepicted transistors 616, 618 are n-type transistors, and one example ofan n-type transistor is an NMOS transistor. The transistor 616 is alsoconnected in series with the transistor 604. A terminal (e.g., S/Dregion) 620 of the transistor 616 and a terminal (e.g., S/D region) 622of the transistor 604 are connected together at node 624. An output lineis connected to the node 624. The terminal (e.g., S/D region) 626 of thetransistor 616 and a terminal (e.g., S/D region) 628 of the transistor618 are connected to a voltage source 630 (e.g., VSS or ground).

The transistors 602, 604, 616, 618 can be constructed with any suitablenumber of fins. Some or all of the transistors 602, 604, 616, 618 aren×m transistors. For example, in one embodiment, the transistors 602,604 are implemented as 2×2 transistors (2 fins, two transistors). Thus,each transistor 602, 604 in FIG. 6 represents two transistors (for atotal of four transistors). In another embodiment, the transistors 602,604 are implemented as 2×4 transistors (2 fins, four transistors), andeach transistor 602, 604 is four transistors (for a total of eighttransistors).

FIG. 7 depicts an example layout of the second combination circuit shownin FIG. 6 in accordance with some embodiments. The example layout 700represents an embodiment where the transistors 602, 604 are implementedas 2×4 transistors (2 fins, four transistors). The layout 700 includesan active diffusion region 702 (e.g., active diffusion region 204 inFIG. 2) disposed in the y direction. As described earlier, the activediffusion region 702 includes one or more fin structures that aredisposed on a substrate (not shown). The illustrated active diffusionregion 702 includes the p-type well region for the p-type transistors602, 604.

Poly lines 704, 706, 708, 710, 712, 714, 716 are disposed over theactive diffusion region 702 in the x direction. Poly lines 704, 710,712, 718 function as the gate A for the four transistors 602 a, 602 b,602 c, 602 d, respectively, (see FIG. 6) in the set 615. The S/D region606 is represented above the poly line 704, below the poly line 718, andbetween the poly lines 710, 712.

The common S/D region 610, 612 is positioned below the poly line 704 andabove the poly line 706, below the poly line 708 and above the poly line710, below the poly line 712 and above the poly line 714, and below thepoly line 716 and above the poly line 718. The common S/D regions 610,612 are the internal nodes 614 a, 614 b, 614 c, 614 d.

The poly lines 706, 708, 714, 716 act as the gate B for the fourtransistors 604 a, 604 b, 604 c, 604 d in the set 615. S/D region(“OUT”) 622 of the four transistors 604 a, 604 b, 604 c, 604 d is shownbelow the poly line 706 and above the poly line 708 and below the polyline 714 and above the poly line 716.

Although not shown in FIG. 7, a first metal layer (e.g., M0 layer) isdisposed over the active region 702 and the poly lines 704, 706, 708,710, 712, 714, 716. The embodiment does not have any connections betweenthe internal nodes 614 a, 614 b, 614 c, 614 d and a common metal stripein the M0 layer. The functions of the transistors 602 a, 602 b, 602 c,602 d, 604 a, 604 b, 604 c, 604 d are the same as conventionaltransistors but connections between the internal nodes 614 a, 614 b, 614c, 614 d and a common metal stripe in the M0 layer are absent. Eachinternal node 614 a, 614 b, 614 c, 614 d is independent of the otherinternal nodes 614 a, 614 b, 614 c, 614 d, and the loading on theinternal nodes 614 a, 614 b, 614 c, 614 d is reduced or eliminated dueto the nonexistent connections between a metal stripe in the M0 layer tothe internal nodes 614 a, 614 b, 614 c, 614 d. Additionally, thetransistors 602 a, 602 b, 602 c, 602 d, 604 a, 604 b, 604 c, 604 d areboth identical and are independent of each other.

FIG. 8 illustrates an example combination circuit that includescascading n-type transistors in accordance with some embodiments. Theexample combination circuit 800 includes a p-type transistor 802connected in parallel with another p-type transistor 804. The terminal(e.g., S/D region) 806 of the transistor 802 and the terminal (e.g., S/Dregion) 808 of the transistor 804 are connected to a voltage source 810(e.g., VSS). The terminal (e.g., S/D region) 812 of the transistor 802and the terminal (e.g., S/D region) 814 of the transistor 804 areconnected together at node 816.

The p-type transistor 802 is connected in series with a set 818 ofcascading n-type transistors 820, 822, 824, 826. The number oftransistors in the set 818 can be any number equal to or greater thantwo. In FIG. 8, the sizing of the cascading n-type transistors 802, 822,824, 826 is (n×m). The number of independent internal nodes in the set818 is (m−1), where (m−1) is equal to or greater than two.

In the illustrated embodiment, a terminal (e.g., S/D region) 828 of thetransistor 820 is connected to the node 816. The terminal (e.g., S/Dregion) 830 of the transistor 820 and the terminal (e.g., S/D region)832 of the transistor 822 are connected together at the internal node834. The ellipses 836 represent zero or more additional transistors inthe set. As such, there are one or more additional internal nodes(collectively referred to as internal node 838). The terminal (e.g., S/Dregion) 840 of the transistor 822 and the terminal (e.g., S/D region)842 of the transistor 824 are connected together at the internal node838. The terminal (e.g., S/D region) 844 of the transistor 824 and theterminal (e.g., S/D region) 846 of the transistor 826 are connectedtogether at the internal node 888. The terminal (e.g., S/D region) 850of the transistor 826 is connected to a voltage source 852 (e.g., VSS orground).

The internal nodes 834, 838, 848 are not connected to a common metalstripe in a metal layer overlying the combination circuit 800 (e.g.,first metal layer 208, second metal layer 210, or third metal layer 212in FIG. 2). As discussed earlier, the absent connections reduce oreliminate the load on the internal nodes 834, 838, 848. Additionally,although the transistors 820, 822, 824, 826 are identical, eachtransistor 820, 822, 824, 826 in the set 818 is independent of the othertransistors 820, 822, 824, 826 in the set 818.

Cascading transistors can be implemented in a variety of combinationcircuits, such as logic circuits and amplifier circuits. The combinationcircuits can include cascading p-type transistors, as shown in FIG. 9.The example fourth combination circuit 900 includes a set 902 ofcascading p-type transistors 904, 906, 908, 910. The number oftransistors in the set 902 can be any number equal to or greater thantwo. Like the embodiment shown in FIG. 8, the sizing of the cascadingp-type transistors 904, 906, 908, 910 is (n×m). The number ofindependent internal nodes in the set 902 is (m−1).

In the illustrated embodiment, a terminal (e.g., S/D region) 912 of thetransistor 904 is connected to a voltage source 914 (e.g., VSS). Theterminal (e.g., S/D region) 916 of the transistor 904 and the terminal(e.g., S/D region) 918 of the transistor 906 are connected together atthe internal node 920. The ellipses 922 represent zero or moreadditional transistors in the set 902. As such, there are one or moreadditional internal nodes (collectively referred to as internal node924). The terminal (e.g., S/D region) 926 of the transistor 906 and theterminal (e.g., S/D region) 928 of the transistor 908 are connectedtogether at an internal node (e.g., internal node 924). The terminal(e.g., S/D region) 930 of the transistor 908 and the terminal (e.g., S/Dregion) 932 of the transistor 932 are connected together at the internalnode 934. The terminal (e.g., S/D region) 936 of the transistor 910 isconnected to the node 938.

The transistor 910 is connected in series with the p-type transistor940. The p-type transistor 940 is connected in parallel with the p-typetransistor 942. The terminal (e.g., S/D region) 936 of the transistor910, the terminal (e.g., S/D region) 944 of the transistor 940, and theterminal (e.g., S/D region) 946 of the transistor 942 are connectedtogether at the node 938. The terminal (e.g., S/D region) 948 of thetransistor 940 and the terminal (e.g., S/D region) 950 of the transistor942 are each connected to a voltage source 952 (e.g., VSS or ground).

The internal nodes 920, 924, 934 are not connected to a common metalstripe in a metal layer overlying the combination circuit 900 (e.g.,first metal layer 208, second metal layer 210, or third metal layer 212in FIG. 2). As discussed earlier, the absent connections reduce oreliminate the load on the internal nodes 920, 924, 934. Additionally,although the transistors 904, 906, 908, 910 are identical, eachtransistor 904, 906, 908, 910 in the set 902 is independent of the othertransistors 904, 906, 908, 910 in the set 902.

FIG. 10 illustrates a flowchart of an example method of designing anintegrated circuit in accordance with some embodiments. Initially, asshown in block 1000, a placement operation is performed to determine thelocations of the components and/or circuits in the cells as well as thelocations of the cells in an IC. Next, as shown in block 1002, a routingscheme for the metal conductors in the IC is determined. In oneembodiment, the routing scheme determines the number of metal layers tobe fabricated to provide signals to and from the components and cells inthe integrated circuit. A schematic diagram of the IC is then producedat block 1004. The schematic diagram is based on the placement of thecomponents/circuits and cells determined at block 1000 and the routingscheme determined at block 1002. Based on the schematic diagram, alayout diagram of the IC is produced at block 1006. The integratedcircuit can be fabricated at block 1008 based on the layout diagram.

In some embodiments, the schematic diagram uses a bus type naming ruleto describe a set of cascading transistors. For example, a bus typenaming rule can be used when a set cascading transistors has a sizedefined by (2fin×m), where m is the number of the cascading transistorsin the set, m is greater than one, and the number of internal nodes isgreater than one. FIG. 11 depicts a set of bus naming rules for athree-input NAND circuit in accordance with some embodiments. FIG. 12illustrates a set of cascading transistors that is defined by the set ofbus naming rules shown in FIG. 11 in accordance with some embodiments.

In FIG. 12, three-input NAND circuit has inputs A, B, and C. Since mequals four (4), and there are three inputs, the set 1101 of bus namingrules shown in FIG. 11 includes twelve (12) names (four (m)×three inputsA, B, C=12) for the twelve transistors that form the three-input NANDcircuit. The gates A for four transistors are connected together, thegates B for four transistors are connected together, and the gates C forfour transistors are connected together.

In FIG. 11, the subset 1100 of names 1102, 1104, 1106, 1108 areassociated with input A (e.g., gate A). The subset 1110 of names 1112,1114, 1116, 1118 are associated with input B (e.g., gate B). The subset1120 of names 1122, 1124, 1126, 1128 are associated with input C (e.g.,gate C). The term “nch” in each name 1102, 1104, 1106, 1108, 1112, 1114,1116, 1118, 1122, 1124, 1126, 1128 indicates the transistors are n-type(n-channel) transistors. The variable m=1 in each name 1102, 1104, 1106,1108, 1112, 1114, 1116, 1118, 1122, 1124, 1126, 1128 shows eachtransistor is an independent single transistor. In other embodiments,additional or fewer names can be included in a subset and/or the numberof subsets may differ from the subsets 1100, 1110, 1120 shown in FIG.11. Additionally or alternatively, in some or all of the names 1102,1104, 1106, 1108, 1112, 1114, 1116, 1118, 1122, 1124, 1126, 1128, theterm “pch” for a p-type (p-channel) transistor can be used instead ofthe term “nch” and/or the variable m can equal a number other than one(1).

The names 1102, 1104, 1106, 1108 define the drain and source connectionsfor each of the four transistors associated with the input A. The fourtransistors having the input A are labeled MN1 , the drains of thetransistors MN1 are labeled OUT, OUT, OUT, OUT, and the sources of thetransistors MN1 are labeled Net_1<3>, Net_1<2>, Net_1<1>, Net_1<0>. Thename 1102 states the drain of the fourth transistor (MN1<3>) having theinput A is connected to OUT and the source of the fourth transistor(MN1<3>) is connected to Net_1<3>. The name 1104 states the drain of thethird transistor (MN1<2>) having the input A is connected to OUT and thesource of the third transistor is connected to MN1<2>is connected toNet_1<2>. The name 1106 states the drain of the second transistor(MN1<1>) having the input A is connected to OUT and the source of secondtransistor (MN1<0>) is connected to Net_1<1>. The name 1108 states thedrain of the first transistor (MN1<0>) having the input A is connectedto OUT and the source of the first transistor (MN1<0>) is connected toNet_1<0>.

The names 1112, 1114, 1116, 1118 define the drain and source connectionsfor each of the four transistors associated with the input B. The fourtransistors having the input B are labeled MN2, the drains of thetransistors MN2 are labeled Net_1<3>, Net_1<2>, Net_1<1>, Net_1<0>, andthe sources of the transistors MN1 are labeled Net_2<3>, Net_2<2>,Net_2<1>, Net_2<0>. The name 1112 states the drain of the fourthtransistor (MN2<3>) having the input B is connected to the source of thefourth transistor (MN1<3>) having the input A. The name 1112 furtherstates the source of the fourth transistor (MN2<3>) having the input Bis connected to Net_2<3>. The name 1114 states the drain of the thirdtransistor (MN2<2>) having the input B is connected to the source of thethird transistor (MN1<2>): having the input A. The name 1114 furtherstates the source of the third transistor (MN2<2>) having the input B isconnected to Net_2<2>. The name 1116 states the drain of the secondtransistor (MN2<1>) having the input B is connected to the source of thesecond transistor (MN1<1>) having the input A. The name 1116 furtherstates the source of the second transistor (MN2<1>) having the input Bis connected to Net_2<1>. The name 1118 states the drain of the firsttransistor (MN2<0>) having the input B is connected to the source of thefirst transistor (MN1<0>) having the input A. The name 1118 furtherstates the source of the first transistor (MN2<0>) having the input B isconnected to Net_2<0 >.

The names 1122, 1124, 1126, 1128 define the drain and source connectionsfor each of the four transistors associated with the input C. The fourtransistors having the input C are labeled MN3, the drains of thetransistors MN3 are labeled Net_2<3 >, Net_2<2 >, Net_2<1 >, Net_2<0 >,and the sources of the transistors MN3 are labeled VSS. The name 1122states the drain of the fourth transistor (MN3<3>) having the input C isconnected to the source of the fourth transistor (MN2<3>) having theinput B, and the source of the fourth transistor (MN3<3>) having theinput C is connected to VSS. The name 1124 states the drain of the thirdtransistor (MN3<2>) having the input C is connected to the source of thethird transistor (MN2<2>) having the input B, and the source of thethird transistor (MN3<2>) having the input C is connected to VSS. Thename 1126 states the drain of the second transistor (MN3<1>) having theinput C is connected to the source of the second transistor (MN2<1>)having the input B, and the source of the second transistor (MN3<1>)having the input C is connected to VSS. The name 1128 states the drainof the first transistor (MN3<0>) having the input C is connected to thesource of the first transistor (MN2<0>) having the input B, and thesource of the fourth transistor (MN3<0>) having the input C is connectedto VSS.

As described earlier, the number of names is based on the number oftransistors that is used to construct a set of cascading transistors.Thus, in other embodiments, the number of names is not limited to twelvenames. For example, in other embodiments the number of names can beeight for eight transistors (number of inputs=2 and m=4) or the numberof names can be four for four transistors (number of inputs=2 and m=2).

In some embodiments, a design for an IC is provided by a computer systemsuch as an Electronic Computer-Aided Design (ECAD) system. ECAD toolsand methods facilitate the design, partition, and placement of circuitsand/or components in an IC on a semiconductor substrate. The ECADprocess typically includes turning a behavioral description of an ICinto a functional description, which is then decomposed into logicfunctions and mapped into cells that implement the logic or otherelectronic functions. Such cells may be defined and stored in a celllibrary. Once mapped, a synthesis is performed to turn the structuraldesign into a physical layout. In some instances, the design may beoptimized post layout.

FIG. 13 depicts an example system that is suitable for designing anintegrated circuit in accordance with some embodiments. The designprocess may be implemented by a computer system, such as an ECAD system.Some or all of the operations for design (e.g., layout) methodsdisclosed herein are capable of being performed as part of a designprocedure performed in a design house, such as the design house 1702discussed below in conjunction with FIG. 17.

In some embodiments, the system 1300 includes an automated place androute (APR) system. In some embodiments, the system 1300 includes aprocessing device 1302 and a non-transitory, computer-readable storagemedium 1304 (“storage device”). The processing device 1302 is anysuitable processing device or processing devices. Example processingdevices include, but are not limited to, a central processing unit, amicroprocessor, a distributed processing system, an application specificintegrated circuit, a graphics processing unit, a field programmablegate array, or combinations thereof.

The storage device 1304 may be encoded with or store, for example,computer program code (e.g., a set of executable instructions 1306).Execution of the executable instructions 1306 by the processing device1302 represents (at least in part) an ECAD tool that implements aportion or all of, the methods described herein to produce the designsfor the structures and the ICs disclosed herein. Further, thefabrication tools 1308 may be included for layout and physicalimplementation of the ICs. In one or more embodiments, the storagedevice 1304 is an electronic, magnetic, optical, electromagnetic,infrared, and/or a semiconductor system (or apparatus or device). Forexample, the storage device 1304 includes a semiconductor or solid-statememory, a magnetic tape, a removable computer diskette, a random accessmemory (RAM), a read-only memory (ROM), a rigid magnetic disk, and/or anoptical disk. In one or more embodiments using optical disks, thestorage device 1304 includes a compact disk-read only memory (CD-ROM), acompact disk-read/write (CD-R/W), and/or a digital video disc (DVD).

The processing device 1302 is operably connected to the storage device1304 via a bus 1310. The processing device 1302 is also operablyconnected to an input/output (I/O) interface 1312 and a networkinterface 1314 by the bus 1310. The network interface 1314 is operablyconnected to a network 1316 so that the processing device 1302 and thestorage device 1304 are capable of connecting to external elements viathe network 1316. In one or more embodiments, the network 1316 isillustrative of any type of wired and/or wireless network, such as anintranet and/or a distributed computing network (e.g., the Internet).

The network interface 1314 allows the system 1300 to communicate withother computing or electronic devices (not shown) via the network 1316.The network interface 1314 includes wireless network interfaces and/orwired network interfaces. Example wireless network interfaces includeBLUETOOTH, WIFI, WIMAX, GPRS, or WCDMA. Example wired network interfacesinclude ETHERNET, USB, or IEEE-1364.In one or more embodiments, some orall of the processes and/or methods disclosed herein are implemented ina distributed system via the network 1316.

The processing device 1302 is configured to execute the executableinstructions 1306 encoded in the storage device 1304 to cause the system1300 to be usable for performing some or all of the processes and/ormethods. For example, an electronic design application (e.g., in an ECADsystem or as a standalone application) can be configured to perform themethods and techniques shown in FIGS. 3-20 and 22. Given the complexityof integrated circuits, and since integrated circuits include thousands,millions, or billions of components, the human mind is unable to performthe methods and techniques depicted in FIGS. 3-20 and 22. Unlike thehuman mind, an electronic design application is able to perform theoperations associated with FIGS. 3-20 and 22.

In one or more embodiments, the storage device 1304 stores theexecutable instructions 1306 configured to cause the system 1300 to beusable for performing some or all of the processes and/or methods. Inone or more embodiments, the storage device 1304 also stores informationthat facilitates execution of a portion of or all of the processesand/or methods. In one or more embodiments, the storage device 1304stores a cell library 1318 that includes (at least in part) standardand/or previously designed cells.

The I/O interface 1312 is operably connected to I/O devices 1320. In oneor more embodiments, the I/O devices 1320 include one or more of animage capture device, a microphone, a scanner, a keyboard, a keypad, amouse, a trackpad, a touchscreen, and/or cursor direction keys forcommunicating information and commands to the processing device 1302.The I/O devices 1320 may also include one or more displays, one or morespeakers, a printer, headphones, a haptic or tactile feedback device,and the like.

The system 1300 is configured to receive information through the I/Ointerface 1312. The information received through the I/O interface 1312includes one or more of instructions, data, design rules, celllibraries, and/or other parameters for processing by the processingdevice 1302. The information is transferred to the processing device1302 via the bus 1310. The system 1300 is configured to receiveinformation related to a user interface (UI) through the I/O interface1312. The information is stored in the storage device 1304 as a UI 1322or for presentation in the UI 1322.

In some embodiments, a portion or all of the processes and/or methods isimplemented as a standalone software application (e.g., an EDA) forexecution by a processing device (e.g., processing device 1302). In someembodiments, a portion or all of the processes and/or methods isimplemented as a software application that is a part of an additionalsoftware application. In some embodiments, a portion or all of theprocesses and/or methods is implemented as a plug-in to a softwareapplication. In some embodiments, at least one of the processes and/ormethods is implemented as a software application that is a portion of anEDA tool. In some embodiments, a portion or all of the processes and/ormethods is implemented as a software application that is used by thesystem 1300. In some embodiments, a layout diagram which includesstandard and/or previously designed cells is generated using a tool suchas VIRTUOSO available from CADENCE DESIGN SYSTEMS, Inc., or anothersuitable layout generating tool.

In some embodiments, the processes are realized as functions of aprogram stored in a non-transitory computer readable recording medium(e.g., the storage device 1304). Examples of a non-transitory computerreadable recording medium include, but are not limited to,external/removable and/or internal/built-in storage or memory unit,e.g., one or more of an optical disk, such as a DVD, a magnetic disk,such as a hard disk, a semiconductor memory, such as a ROM, a RAM, amemory card, and the like.

As noted above, embodiments of the system 1300 may include thefabrication tools 1308 for implementing the processes and/or methodsstored in the storage device 1304. For instance, a synthesis may beperformed on a design in which the behavior and/or functions desiredfrom the design are transformed to a functionally equivalent logicgate-level circuit description by matching the design to cells selectedfrom the cell library 1318. The synthesis results in a functionallyequivalent logic gate-level circuit description, such as a gate-levelnetlist. Based on the gate-level netlist, a photolithographic mask maybe generated that is used to fabricate the IC by the fabrication tools1308. Further aspects of device fabrication are disclosed in conjunctionwith FIG. 17, which is a block diagram of an integrated circuitmanufacturing system, and a manufacturing flow associated therewith, inaccordance with some embodiments. In some embodiments, based on a layoutdiagram, at least one of: (a) one or more semiconductor masks; or (b) atleast one component in a layer of a semiconductor IC is fabricated usingthe manufacturing system 1700.

FIG. 14 illustrates a flowchart of an example method of fabricating aset of cascading transistors in accordance with some embodiments.Initially, a schematic diagram of an IC is received at block 1400. Theschematic diagram defines a set of cascading transistors using the bustype naming rule described in conjunction with FIG. 11. Next, a layoutdiagram for the IC is generated at block 1402. The layout diagramincludes geometrical patterns, or a layout diagram for the set ofcascading transistors.

The integrated circuit is fabricated at block 1403 using the layoutdiagram. Fabrication of the IC includes fabricating one or more circuitsthat operably connect to the set of cascading transistors andfabricating the set of cascading transistors. The process of fabricatingthe set of cascading transistors in block 1405 begins with forming achannel layer over a substrate at block 1404. Any suitable method can beused to form the channel layer. For example, the channel layer can bedeposited over the substrate. Additionally, any suitable substrate canbe used. An example substrate includes, but is not limited to, a siliconsubstrate, a gallium arsenide substrate, a silicon-on-insulatorsubstrate, a gallium nitride substrate, and a silicon carbide substrate.

Next, as shown in block 1406, the channel layer is doped with one ormore dopants, such as one or more n-type dopants or one or more p-typedopants. An isolation layer is then formed over the doped channel layer(block 1408). Any suitable method can be used to form the isolationlayer. For example, the isolation layer can be deposited over the dopedchannel layer.

A polysilicon (“poly”) layer is formed over the isolation layer at block1410. The poly layer is used to form the gates of the transistors in theset of cascading transistors. Any suitable method can be used to formthe poly layer. For example, the poly layer can be deposited over theisolation layer.

The poly layer, the isolation layer, and the doped channel layer arethen patterned to produce openings that expose a surface of thesubstrate (block 1412). The patterning of the poly layer produces thegates of the transistors in the set of cascading transistors. Anysuitable method or methods can be used to pattern poly layer, theisolation layer, and the doped channel layer. For example, in oneembodiment, a mask layer is formed over the poly layer, the isolationlayer, and the doped channel layer and developed to define the locationsof the openings. The poly layer, the isolation layer, and the dopedchannel layer are then etched to produce the openings.

In another embodiment, a first mask layer is formed over the poly layerand developed to define the locations of the openings and the poly layeris then etched to produce openings in the poly layer. A second masklayer is then formed over the poly layer and developed to define thelocations of the openings and the isolation layer is etched to produceopenings in the isolation layer. The locations of the openings in theisolation layer substantially align with the openings in the poly layer.A third mask layer is then formed over the poly layer and developed todefine the locations of the openings and the doped channel layer isetched to produce openings in the doped channel layer. The locations ofthe openings in the doped channel layer substantially align with theopenings in the isolation and poly layers.

Next, as shown in block 1414, a source region or a drain region isformed in respective openings. A stack of metal layers is then formedabove the set of cascading transistors (block 1416). Each metal layerincludes metal stripes. The internal nodes in the set of cascadingtransistors are operably connected to a respective metal stripe in onemore of the metal layers (block 1418). The internal nodes are notconnected to the same metal stripe (e.g., a common metal stripe) in anyof the metal layers.

FIG. 15 depicts the set of cascading transistors shown in FIG. 4 afterthe method of FIG. 14 is performed in accordance with some embodiments.In particular, the set of cascading transistors are shown after blocks1400, 1402, 1404, 1406, 1408, 1410, 1412, and 1414 have been performed.As described previously, m=4 for the set 415 of cascading transistorsand there are two inputs (input A, input B). Thus, eight transistors(2×4) are fabricated for the set 415.

FIG. 16 illustrates the set of cascading transistors shown in FIG. 6after the method of FIG. 14 is performed in accordance with someembodiments. In particular, the set of cascading transistors are shownafter blocks 1400, 1402, 1404, 1406, 1408, 1410, 1412, and 1414 havebeen performed. As described earlier, m=4 for the set 615 of cascadingtransistors and there are two inputs (input A, input B). Thus, eighttransistors (2×4) are fabricated for the set 615.

FIG. 17 depicts a block diagram of an example integrated circuitmanufacturing system and manufacturing flow in accordance with someembodiments. In the illustrated embodiment, the IC manufacturing system1700 includes entities, such as a design house 1702, a mask house 1704,and an IC manufacturer/fabricator (“fab”) 1706, that interact with oneanother in the design, development, and manufacturing cycles and/orservices related to manufacturing an IC 1708, such as the ICs disclosedherein. The entities in the system 1700 are operably connected by acommunication network (not shown). In some embodiments, thecommunication network is a single network. In some embodiments, thecommunication network is a variety of different networks, such as anintranet and the Internet. The communication network includes wiredand/or wireless communication channels.

Each entity interacts with one or more of the other entities andprovides services to and/or receives services from one or more of theother entities. In some embodiments, two or more of the design house1702, the mask house 1704, and the IC fab 1706 is owned by a singlecompany. In some embodiments, two or more of the design house 1702, themask house 1704, and the IC fab 1706 coexist in a common facility anduse common resources.

The design house (or design team) 1702 generates an IC design layoutdiagram 1710. As described earlier, the IC design layout diagram 1710 istypically created based on a schematic diagram of the IC, and theschematic diagram can include a set of names that conform to the bustype naming rule described in conjunction with FIG. 11. The IC designlayout diagram 1710 includes various geometrical patterns, or IC layoutdiagrams designed for the IC 1708 to be fabricated. The geometricalpatterns correspond to patterns of metal, oxide, or semiconductor layersthat make up the various components of the IC 1708 to be fabricated. Thevarious layers combine to form various IC features. For example, aportion of the IC design layout diagram 1710 includes various ICfeatures, such as active diffusion regions, gate electrodes, source anddrain, metal lines, metal stripes, or local vias, and openings forbonding pads, to be formed in a semiconductor substrate (such as asilicon wafer) and various material layers disposed on the semiconductorsubstrate.

The design house 1702 implements a design procedure to form the ICdesign layout diagram 1710. The design procedure includes one or more oflogic design, physical design or place and route. The IC design layoutdiagram 1710 is presented in one or more data files having informationof the geometrical patterns. For example, the IC design layout diagram1710 can be expressed in a GDS file format, a GDSII file format, or aDFII file format.

The mask house 1704 includes mask data preparation 1712 and maskfabrication 1714. The mask house 1704 uses the IC design layout diagram1710 to manufacture one or more masks 1716 to be used for fabricatingthe various layers of the IC 1708 according to the IC design layoutdiagram 1710. The mask house 1704 performs mask data preparation 1712,where the IC design layout diagram 1710 is translated into arepresentative data file (“RDF”). The mask data preparation 1712provides the RDF to the mask fabrication 1714. The mask fabrication 1714includes a mask writer (not shown) that converts the RDF to an image ona substrate, such as a mask (reticle) 1716 on a semiconductor wafer. TheIC design layout diagram 1710 is manipulated by the mask datapreparation 1712 to comply with particular characteristics of the maskwriter and/or requirements of the IC fab 1706. In FIG. 17, the mask datapreparation 1712 and the mask fabrication 1714 are illustrated asseparate elements. In some embodiments, the mask data preparation 1712and the mask fabrication 1714 can be collectively referred to as a maskdata preparation.

In some embodiments, the mask data preparation 1712 includes an opticalproximity correction (OPC) that uses lithography enhancement techniquesto compensate for image errors, such as those that can arise fromdiffraction, interference, other process effects and the like. The OPCadjusts the IC design layout diagram 1710. In some embodiments, the maskdata preparation 1712 includes further resolution enhancement techniques(RET), such as off-axis illumination, sub-resolution assist features,phase-shifting masks, other suitable techniques, and the like orcombinations thereof. In some embodiments, inverse lithographytechnology (ILT) is also used, which treats OPC as an inverse imagingproblem.

In some embodiments, the mask data preparation 1712 includes a mask rulechecker (MRC) (not shown) that checks the IC design layout diagram 1710that has undergone processes in OPC with a set of mask creation rulesthat contain certain geometric and/or connectivity restrictions toensure sufficient margins, to account for variability in semiconductormanufacturing processes, and the like. In some embodiments, the MRCmodifies the IC design layout diagram 1710 to compensate for limitationsduring the mask fabrication, which may undo part of the modificationsperformed by OPC in order to meet mask creation rules.

In some embodiments, the mask data preparation 1712 includes lithographyprocess checking (LPC) (not shown) that simulates processing that willbe implemented by the IC fab 1706 to fabricate the IC 1708. LPCsimulates this processing based on the IC design layout diagram 1710 tocreate a simulated manufactured device, such as the IC 1708. Theprocessing parameters in LPC simulation can include parametersassociated with various processes of the IC manufacturing cycle,parameters associated with tools used for manufacturing the IC, and/orother aspects of the manufacturing process. LPC takes into accountvarious factors, such as aerial image contrast, depth of focus (“DOF”),mask error enhancement factor (“MEEF”), other suitable factors, and thelike or combinations thereof. In some embodiments, after a simulatedmanufactured device has been created by LPC, and if the simulated deviceis not sufficiently close in shape to satisfy design rules, OPC and/orMRC are be repeated to further refine the IC design layout diagram 1710.

It should be understood that the above description of the mask datapreparation 1712 has been simplified for the purposes of clarity. Insome embodiments, the mask data preparation 1712 includes additionalfeatures such as a logic operation (LOP) to modify the IC design layoutdiagram 1710 according to manufacturing rules. Additionally, theprocesses applied to the IC design layout diagram 1710 during the maskdata preparation 1712 may be executed in a variety of different orders.

After the mask data preparation 1712 and during the mask fabrication1714, a mask 1716 or a group of masks 1716 are fabricated based on theIC design layout diagram 1710. In some embodiments, the mask fabrication1714 includes performing one or more lithographic exposures based on theIC design layout diagram 1710. In some embodiments, an electron-beam(e-beam) or a mechanism of multiple e-beams is used to form a pattern ona mask(s) 1716 (photomask or reticle) based on the IC design layoutdiagram 1710. The mask(s) 1716 can be formed in various technologies.For example, in some embodiments, the mask(s) 1716 is formed usingbinary technology. In some embodiments, a mask pattern includes opaqueregions and transparent regions. A radiation beam, such as anultraviolet (UV) beam, used to expose the image sensitive material layer(e.g., photoresist) which has been coated on a wafer, is blocked by theopaque region and transmits through the transparent regions. In oneexample, a binary mask version of the mask(s) 1716 includes atransparent substrate (e.g., fused quartz) and an opaque material (e.g.,chromium) coated in the opaque regions of the binary mask.

In another example, the mask(s) 1716 is formed using a phase shifttechnology. In a phase shift mask (PSM) version of the mask(s) 1716,various features in the pattern formed on the phase shift mask areconfigured to have a proper phase difference to enhance the resolutionand imaging quality. In various examples, the phase shift mask can beattenuated PSM or alternating PSM. The mask(s) 1716 generated by themask fabrication 1714 is used in a variety of processes. For example, amask(s) 1716 is used in an ion implantation process to form variousdoped regions in the semiconductor wafer, in an etching process to formvarious etching regions in the semiconductor wafer, and/or in othersuitable processes.

The IC fab 1706 includes wafer fabrication 1718. The IC fab 1706 is anIC fabrication business that includes one or more manufacturingfacilities for the fabrication of a variety of different IC products. Insome embodiments, the IC fab 1706 is a semiconductor foundry. Forexample, there may be a manufacturing facility for the front endfabrication of a plurality of IC products (FEOL fabrication), while asecond manufacturing facility may provide the back end fabrication forthe interconnection and packaging of the IC products (BEOL fabrication),and a third manufacturing facility may provide other services for thefoundry business.

The IC fab 1706 uses the mask(s) 1716 fabricated by the mask house 1704to fabricate the IC 1708. Thus, the IC fab 1706 at least indirectly usesthe IC design layout diagram 1710 to fabricate the IC 1708. In someembodiments, a semiconductor wafer 1720 is fabricated by the IC fab 1706using the mask(s) 1716 to form the IC 1708. In some embodiments, the ICfab 1706 includes performing one or more lithographic exposures based atleast indirectly on the IC design layout diagram 1710. The semiconductorwafer 1720 includes a silicon substrate or other proper substrate havingmaterial layers formed thereon. The semiconductor wafer 1720 furtherincludes one or more of various doped regions, dielectric features,multilevel interconnects, and the like (formed at subsequentmanufacturing steps).

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

In one aspect, a combination circuit includes a set of cascadingtransistors having a first internal node and a second internal nodeformed in an active region, and a stack of metal layers disposed overthe active region and the set of cascading transistors. The activeregion includes at least one of a p-type well and an n-type well. Eachmetal layer in the stack of metal layers includes a plurality of metalstripes, and the first and the second internal nodes are not connected acommon metal stripe in the stack of metal layers.

In another aspect, an integrated circuit includes a set of cascadingtransistors having multiple internal nodes that are formed in an activeregion that comprises at least one of a p-type well or an n-type well,and a metal layer disposed over the active region and the set ofcascading transistors. A number of transistors in the set of cascadingtransistors is (m), where m is greater than two. The metal layerincludes a plurality of metal stripes and the multiple internal nodesare not connected a common metal stripe in the metal layer.

In yet another aspect, a method of fabricating a set of cascadingtransistors in an integrated circuit includes receiving a schematicdiagram for the integrated circuit and generating a layout diagram forthe integrated circuit. The schematic includes a set of names for thetransistor in the set of cascading transistor that conform to a bus typenaming rule. The layout diagram including a layout for the set ofcascading transistors. Based on the layout diagram for the integratedcircuit, the integrated circuit is fabricated, including the set ofcascading transistors. Fabricating the set of cascading transistorsincludes forming a doped channel layer over a substrate, forming anisolation layer over the doped channel layer, and forming a polysiliconlayer over the isolation layer. The doped channel layer, the isolationlayer, and the polysilicon layer are patterned to produce a plurality ofopenings, where each opening exposes a surface of the substrate and thepatterning of the polysilicon layer forms gates for the transistors inthe set of cascading transistors. A source region or a drain region isformed in respective openings in the plurality of openings.

The description and illustration of one or more aspects provided in thisapplication are not intended to limit or restrict the scope of thedisclosure as claimed in any way. The aspects, examples, and detailsprovided in this application are considered sufficient to conveypossession and enable others to make and use the best mode of claimeddisclosure. The claimed disclosure should not be construed as beinglimited to any aspect, example, or detail provided in this application.Regardless of whether shown and described in combination or separately,the various features (both structural and methodological) are intendedto be selectively included or omitted to produce an embodiment with aparticular set of features. Having been provided with the descriptionand illustration of the present application, one skilled in the art mayenvision variations, modifications, and alternate aspects falling withinthe spirit of the broader aspects of the general inventive conceptembodied in this application that do not depart from the broader scopeof the claimed disclosure.

What is claimed is:
 1. A combination circuit, comprising: a set ofcascading transistors that include a first internal node and a secondinternal node formed in an active region, the active region including atleast one of a p-type well or an n-type well; and a stack of conductivelayers disposed over the active region and the set of cascadingtransistors, wherein each conductive layer in the stack of conductivelayers comprises a plurality of conductive stripes and the first and thesecond internal nodes are not connected a common conductive stripe inthe stack of conductive layers, the common conductive stripe comprisinga single conductive stripe in the stack of conductive layers.
 2. Thecombination circuit of claim 1, wherein the combination circuitcomprises a NAND circuit.
 3. The combination circuit of claim 1, whereinthe combination circuit comprises a NOR circuit.
 4. The combinationcircuit of claim 1, wherein the first internal node is connected to afirst metal stripe in a first metal layer and the second internal nodeis connected to a different second metal stripe in the first metallayer.
 5. The combination circuit of claim 1, wherein the set ofcascading transistors is a set of cascading n-type transistors or a setof cascading p-type transistors.
 6. The combination circuit of claim 1,wherein the plurality of conductive stripes comprise metal stripes.
 7. Acombination circuit, comprising: a set of cascading transistors thatinclude a first internal node and a second internal node formed in anactive region, the active region including at least one of a p-type wellor an n-type well; and a metal layer disposed over the active region andthe set of cascading transistors, wherein the metal layer comprises aplurality of metal stripes and the first and the second internal nodesare not connected a common metal stripe in the metal layer.
 8. Thecombination circuit of claim 7, wherein the combination circuitcomprises a NAND circuit.
 9. The combination circuit of claim 7, whereinthe combination circuit comprises a NOR circuit.
 10. The combinationcircuit of claim 7, wherein the first internal node is connected to afirst metal stripe in a first metal layer and the second internal nodeis connected to a different second metal stripe in the first metallayer.
 11. The combination circuit of claim 7, wherein the set ofcascading transistors is a set of cascading n-type transistors or a setof cascading p-type transistors.
 12. A method of fabricating a set ofcascading transistors in an integrated circuit, the method comprising:receiving a schematic diagram for the integrated circuit, the schematicdiagram including a set of names for transistors in the set of cascadingtransistors that conform to a bus type naming rule; generating a layoutdiagram for the integrated circuit, the layout diagram including alayout diagram for the set of cascading transistors; and based on thelayout diagram for the integrated circuit, fabricating the integratedcircuit including the set of cascading transistors, wherein fabricatingthe set of cascading transistors comprises: forming a doped channellayer over a substrate; forming an isolation layer over the dopedchannel layer; forming a polysilicon layer over the isolation layer;patterning the doped channel layer, the isolation layer, and thepolysilicon layer to produce a plurality of openings, wherein eachopening exposes a surface of the substrate and the patterning of thepolysilicon layer forms gates for the transistors in the set ofcascading transistors; forming a source region or a drain region inrespective openings in the plurality of openings; and forming a stack ofconductive layers over the set of cascading transistors.
 13. The methodof claim 12, further comprising: prior to forming the doped channellayer over the substrate, forming a channel layer over the substrate;and doping the channel layer with one or more dopants to produce thedoped channel layer.
 14. The method of claim 13, wherein the one or moredopants comprise one or more n-type dopants.
 15. The method of claim 13,wherein the one or more dopants comprise one or more p-type dopants. 16.The method of claim 12, further comprising forming a stack of metallayers over the set of cascading transistors, each metal layer includinga plurality of metal stripes.
 17. The method of claim 15, furthercomprising forming a connection between each internal node in the set ofcascading transistors and a metal stripe in one or more metal layer inthe stack of metal layers, wherein each internal node is not connectedto a common metal stripe in the stack of metal layers, the common metalstripe comprising a single metal stripe in the stack of metal layers.18. The method of claim 12, wherein fabricating the integrated circuitfurther comprises fabricating one or more circuits that operably connectto the set of cascading transistors.
 19. The method of claim 12, whereinthe set of cascading transistors is a set of cascading p-typetransistors.
 20. The method of claim 12, wherein the set of cascadingtransistors is a set of cascading n-type transistors.